This invention relates generally to apparatus for the removal of odorous constituents from gas streams. More particularly, this invention relates to an apparatus for the extended contact of very finely divided liquid droplets with a gas stream whereby the odorous constituents react with the reagent droplets to purify the gas.
Offensive odors which are characteristic of many chemical process industries are often difficult and costly to eliminate or control. Examples include rendering plants, dog food producers, sewage sludge digestion plants, flavors and fragrances production and fermentation processes. Although there are presently no federal regulations for odor control, local laws are often sufficiently stringent to enable authorities to act on complaints and levy stiff fines or, in some cases, even close plants.
There have been a number of approaches taken to the control of odors. Possibly the simplest has been merely to dilute the odorous gas with large quantities of air and hope for the best. Attempts have been made to mask offensive odors with more pleasant ones, but this approach has not been particularly successful as the new odor mixture also was unpleasant or the improved odor could not be sustained. A more radical approach to odor control has been by incineration. This is often a very costly approach as the entire odorous gas stream must be subjected to combustion temperatures.
Another common approach to odor control is by chemical neutralization of the odorous compounds. The odorous gas is conventionally washed with an aqueous solution of a reactive chemical in spray towers, packed beds and the like. Chemical agents commonly used for this purpose include permanganates, dichromates, acids, hypochlorite solutions, hydrogen peroxide and other common oxidizing agents. Exemplary processes are described in British Pat. No. 1,152,705 and in U.S. Pat. No. 3,923,955.
Another technique for the chemical neutralization of odors is described in copending commonly assigned patent application Ser. No. 649,696, now U.S. Pat. No. 4,125,589. That application describes introducing odorous gases such as those produced in rendering operations into the top of a relatively large open tower. An aqueous solution of an oxidizing agent such as hypochlorite is introduced into the tower through nozzles in the form of a very finely-divided spray. Sizing of the tower is adjusted to the gas flow rate so that an extended contact time between the reagent droplets and the gas is achieved. Because of the vast effective surface area generated by the finely-divided droplets, essentially complete removal of chemically reactive odorous constituents is achieved in a single stage treatment. However, because of the relatively large reactor required by this process, field construction and assembly can present difficulties.